With demand for size shrinking of a pattern formed on a sample in a semiconductor process in recent years, improvement of the overlay precision of patterns over a plurality of layers of an exposure device is demanded. It is considered to become increasingly important to measure overlay with high precision and feedback the measured overlay to the exposure device. In a conventional main stream, an optical overlay measuring device is used in overlay measurement. In the optical overlay measuring device, however, there is a measuring precision limit and a wide pattern area is needed for overlay measurement. Furthermore, in principle, it is difficult for the optical overlay measuring device to detect overlay deviation caused by high-order distortion in the exposure device.
On the other hand, a charged particle beam device such as a scanning electron microscope can acquire a high resolution image of a high magnification, and consequently deviation between layers can be measured accurately.
In Patent Literature 1, a technique of measuring a dimension between patterns belonging to a plurality of layers by using a scanning electron microscope (SEM) is described. According to a measurement method as disclosed in Patent Literature 1, an image representing an actual pattern which is actually formed can be used, and consequently a dimension between patterns can be measured with very high precision.
In Patent Literature 2, an overlay vernier for aligning between an upper layer and a lower layer on a wafer and a semiconductor device manufacturing method using the overlay vernier are disclosed.